1. Field of the Invention
This invention generally relates to devices for conditioning the temperature and pressure of fluids and particularly to valves which simultaneously reduce the temperature and pressure of superheated steam by injecting cooling fluid into the valve which fluid is mixed with the stream flowing through the valve during the pressure reduction stage.
2. Description of the Prior Art
Heretofore it has been customary to condition superheated steam by subjecting the steam first to a pressure drop in an appropriate pressure reducing valve and then to inject desuperheating water into the steam after it leaves the pressure reducing valve. That is, the temperature-reducing water was introduced into the steam downstream from the steam pressure-reducing valve. This method required the connection of a long extent of pipe downstream to the valve outlet wherein cold water could be sprayed through a temperature controlled valve and a spray nozzle structure. It is also known to spray cooling water into the throat area of the pressure-reducing valve to allow the mixing of steam and water to occur downstream in a straight run portion of pipe.
These prior art arrangements suffered the disadvantage of having a relatively long section or run of pipe downstream from the pressure-reducing valve making the arrangement bulky and expensive. These prior art arrangements also displayed other problems such as difficulty in attaining uniform mixing of the cooling water with the steam, inefficient heat transfer, tendency toward noisy operation, requirement for interstage pressure taps on the feedwater pump, difficulty in controlling the turndown ratio, requirement for desuperheaters, high alloy steel downstream pipelines, bypass valves, etc., all of which have required costly equipment and have left much to be desired in function and results.
Recently steam conditioning valves have been developed which simultaneously reduce the temperature and pressure of the steam by introducing the temperature reducing water upstream of the valve and allowing the steam and water to be mixed in a disk stack labyrinth structure located in the valve. Examples of such labyrinth structures used in such valves may be found in U.S. Pat. No. 3,513,864 and 3,514,074 issued to Richard E. Self. These labyrinth structures reduce the steam pressure and provide excellent mixing between the steam and water to also reduce the steam temperature. An example of such a known steam conditioning valve may be found in U.S. Pat. No. 3,732,851 issued to Richard E. Self.
The above-mentioned steam conditioning valve has a cooling water spray orifice formed in a movable plug member used to control the flow of steam into the labyrinth structure. As such the orifice moves with the plug member and cannot be supplied with cooling water from any rigid stationary water supply line. Instead, the valve housing on the side of the plug member opposite the orifice is formed as a variable volume water supply chamber which is in continuous communication with the plug member orifice through a passageway extending through the plug member. The water supply chamber, however, cools that part of the valve housing enclosing the supply chamber and produces temperature gradients between the high temperature steam inlet side of the valve housing and the low temperature water supply chamber side of the valve housing. Thermal stresses are thereby produced in the valve which may cause cracking of the valve housing from thermal fatigue.